The Tropic of Cancer, which is also referred to as the Northern tropic, is the circle of latitude on the Earth that serves as a marker for the most northerly position at which the sun may appear directly overhead at its zenith. This event happens once per year, at the time of the June solstice, when the Northern Hemisphere is tilted towards the Sun to its maximum degree.
Its Southern Hemisphere counterpart, marking the most southerly position at which the Sun might appear directly...

A prime meridian is a meridian, i.e. a line of longitude, at which the definition of longitude is zero degrees. A prime meridian and its opposite in a 360 degree-system, the 180th meridian, create a great circle.
This great circle separates the sphere into two hemispheres. If one uses directions f East and West from a defined prime meridian, then they can be named Eastern and Western Hemisphere.
A prime meridian is eventually arbitrary, unlike an equator, which is determined by the axis...

An equator is the intersection of a sphere’s surface with the plane that is perpendicular to the sphere’s axis of rotation and midway between the poles. The Equator is normally referred to the Earth’s equator: an imaginary line on the Earth’s surface halfway between the North Pole and the South Pole, separating the Earth into the Northern Hemisphere and Southern Hemisphere. Other planets and astronomical bodies have equators that are similarly defined. The Equator is approximately...

A foghorn, most often used in foggy conditions, is a device that uses sound to warn vehicles of hazards. Generally the term is used in marine transport. When lighthouses are obscured the foghorn provides an audible warning of any dangers to ships. They have been used for hundreds of years with some of the initial ones being simple bells or gongs that were manually struck. Some lighthouses shot off cannons periodically in order to warn ships. Whistles were also used in the early days....

The compass is a tool that helps the user navigate using the Earth's magnetic poles by using a magnetized pointer that reacts to magnetic fields. Since a compass can be used to calculate a heading it quickly improved the safety and efficiency of travel, especially ocean travel. It has only recently been replaced by Global Positioning Systems. It works by indicating the direction of the magnetic north of a planet's magnetosphere. Generally the face of a compass highlights the north, south,...

A pivoted catch designed to fall into a notch on a ratchet wheel so as to allow movement in only one direction (e.g. on a windlass or in a clock mechanism), or alternatively to move the wheel in one direction.